1. Field of the Invention
The present invention relates to a flat double-spiral lamp.
2. Related Art
FIG. 1 shows a lamp 600 having an arc tube 610 in which a discharge path turns in a double spiral, as one well-known type of compact lamps (German Patent No. 871927). This lamp 600 is a single-based lamp, with both tube ends 611 of the arc tube 610 being held by a holder 630 equipped with a base 620 and a pair of electrodes (not illustrated) sealed at both tube ends 611 being electrically connected to the base 620.
FIG. 2 shows a lamp 700 having an arc tube 710 in which a discharge path turns in a double spiral substantially on one plane (disclosed in Japanese Patent Application Publication No. H09-45283. Note that this type of lamp has not yet been put in practical use). This lamp 700 is thinner than the lamp 600 shown in FIG. 1, because the arc tube 710 is substantially a disc in outside shape whereas the arc tube 610 is substantially a cone in outside shape. Such a lamp 700 allows a lamp fixture to be made thinner, and so is suitable as a light source of a downlight or a wall light recessed in a ceiling or a wall. Also, the lamp 700 is a surface light source having a circular light emitting surface, and so exhibits a favorable light distribution on an irradiated surface. Hence the lamp 700 is suitable for store or home lighting.
As shown in FIG. 2, the lamp 700 is a double-based lamp that is equipped with separate bases 720a and 720b at both tube ends 711a and 711b of the arc tube 710. This being so, if an excessive force is applied when inserting the bases 720a and 720b into sockets of a lamp fixture, the arc tube 710 may be broken near the tube end 711a or 711b. Besides, to attach the lamp 700 to the lamp fixture, the arc tube 710 needs to be held by hand, which causes a sense of worry about breaking the arc tube 710.
To assume a circular light emitting surface, the arc tube 710 is designed so as to minimize a gap 712 between adjacent turns in a spiraled portion between the tube ends 711a and 711b. This being the case, when an inner part of the spiraled portion vibrates due to an external impact, adjacent turns in that part may collide with each other, as a result of which the arc tube 710 can be broken. This tends to occur particularly during transportation. With a conventional transportation container that holds only outer edges of the arc tube 710, such vibrations of the inner part of the spiraled portion cannot be prevented.